Projectors have been around for quite some time. Historically, they projected only static images. The image to be projected would be placed a horizontal surface above a light source. Mirrors would then reflect the image onto a vertical surface parallel to the front of the projector, for easy viewing. The image could be raised or lowered by changing the angle of the mirror, and could be focused by raising or lowering the mirror (thereby changing the focal length of the projector).
With the advent of computers, manufacturers realized that projectors might be able to project dynamic (that is, changing) images. The first ventures in this area relied separate boxes that were placed on top of the light source, where the static images would have been placed. The computer was then responsible for changing the image in the box; the projector would show dynamic images by virtue of its light and mirror system.
Eventually, projector manufacturers realized that the two pieces could be combined. The projectors could connect directly to the computer and place the dynamic images directly in front of the light source, without requiring separate equipment. Projectors eventually moved from indirect (that is, reflected) projection systems to direct projection systems, where the image is oriented vertically, in a plane parallel to the projection surface.
But all of these systems suffered from a common problem. They all expect that the image, as projected, will be shown on a surface that is parallel to the front face of the projector. If the surface onto which the image is projected is not parallel to the front face of the projector, the image is distorted.
Various improvements to projectors have been made, to attempt to address this problem. For example, U.S. Pat. Nos. 6,520,547, 6,367,933, 6,305,805, and 6,339,434 each attempt to solve the problem. But each of these patents fails to completely solve the problem. U.S. Pat. No. 6,520,547, which uses 3×3 rotation matrices, does not work in a digital environment. U.S. Pat. No. 6,367,933 assumes that the optical axis of the projector is centered relative to the projected image, which is not usually the case. U.S. Pat. No. 6,305,805 warps the image by adding or deleting pixels, which is not an acceptable practice. And U.S. Pat. No. 6,339,434 only describes a scaling system in general.
Accordingly, a need remains for a way to correct for image distortion that addresses these and other problems associated with the prior art.